Efficiency analysis of helium-cooled MAS DNP: case studies of surface-modified nanoparticles and homogeneous small-molecule solutions
Efficiency analysis of helium-cooled MAS DNP: case studies of surface-modified nanoparticles and homogeneous small-molecule solutions
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DOI：
10.1039/d0cp05658h
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发表时间：
2021-02-28
影响因子：
3.3
通讯作者：
Fujiwara, Toshimichi
中科院分区：
文献类型：
--
作者：
Matsuki, Yoh;Kobayashi, Takeshi;Fujiwara, Toshimichi
尽管动态核极化（DNP）增强魔角自旋（MAS）NMR在结构生物学和材料科学中的成功应用越来越多，但当前MAS DNP仪器实现的核极化仍然大大低于理论最大值。如果实验在远低于目前广泛使用的温度（类似于100 K）下进行，则该方法可以得到显著加强。最近，氦（He）冷却MAS DNP的前景已经增加了MAS技术，使用冷氦气冷却样品的仪器的发展。尽管已经观察到与氦冷却MAS DNP的灵敏度的额外收益，该技术的性能尚未在表面和界面的情况下，从DNP受益最多的评估。在此，我们研究了在磁场B-0 = 16.4 T下，有机官能化二氧化硅材料和有机小分子的均匀溶液在类似于30 K和类似于100 K之间的温度下的DNP效率。我们记录了信号增强，顺磁诱导的淬灭和去极化效应，DNP建立率，和玻尔兹曼极化的变化。对于这些样品，MAS诱导的去极化和DNP建立时间在30 K左右的增加并不像预期的那样严重。在表面物种的情况下，我们确定，MAS DNP在30 K提供类似的10倍以上的灵敏度比MAS DNP在90 K，这对应于加速实验的乘法因子高达100。
Despite the growing number of successful applications of dynamic nuclear polarization (DNP)-enhanced magic-angle spinning (MAS) NMR in structural biology and materials science, the nuclear polarizations achieved by current MAS DNP instrumentation are still considerably lower than the theoretical maximum. The method could be significantly strengthened if experiments were performed at temperatures much lower than those currently widely used (similar to 100 K). Recently, the prospects of helium (He)-cooled MAS DNP have been increased with the instrumental developments in MAS technology that uses cold helium gas for sample cooling. Despite the additional gains in sensitivity that have been observed with He-cooled MAS DNP, the performance of the technique has not been evaluated in the case of surfaces and interfaces that benefit the most from DNP. Herein, we studied the efficiency of DNP at temperatures between similar to 30 K and similar to 100 K for organically functionalized silica material and a homogeneous solution of small organic molecules at a magnetic field B-0 = 16.4 T. We recorded the changes in signal enhancement, paramagnet-induced quenching and depolarization effects, DNP build-up rate, and Boltzmann polarization. For these samples, the increases in MAS-induced depolarization and DNP build-up times at around 30 K were not as severe as anticipated. In the case of the surface species, we determined that MAS DNP at 30 K provided similar to 10 times higher sensitivity than MAS DNP at 90 K, which corresponds to the acceleration of experiments by multiplicative factors of up to 100.